Create Binary Tree From Descriptions - Map & Set

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Description

Solution: Map & Set

Use a map 'nodes' to store the references to the tree nodes.
Use a set 'children' to store the values of all children nodes.
This is used to find the root, the root node is the only node that does not exist in the set.

Time Complexity: O(n) 510ms
Space Complexity: O(n) 88.8MB

var createBinaryTree = function(descriptions) {
  let nodes = new Map(), children = new Set();
  for (let [parent, child, isLeft] of descriptions) {
    let parentNode = nodes.get(parent) || new TreeNode(parent);
    if (!nodes.has(parent)) nodes.set(parent, parentNode);
    
    let childNode = nodes.get(child) || new TreeNode(child);
    if (!nodes.has(child)) nodes.set(child, childNode);
    
    if (isLeft) parentNode.left = childNode;
    else parentNode.right = childNode;
    
    children.add(child);
  }

  for (let [parent, child, isLeft] of descriptions) {
    // a node with no parent is the root
    if (!children.has(parent)) return nodes.get(parent);
  }
};

javascript
Location: Auckland, New Zealand

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